Nozzles commonly are employed in plastic injection molding machines for heating and directing the flow stream, such as molten plastic, through a gate into a mold cavity while maintaining the flow stream at the proper elevated temperature. Nozzles, sometimes referred to as valve gate nozzles, are known which each include a valve pin movable by an actuator for opening and closing the valve gate at the nozzle tip during each cycle of the molding operation Such valve gate nozzles may be employed in single cavity molds, or alternatively, a series of nozzles may be used in multiple cavity molds. The valve pin actuating means for such valve gate nozzles heretofore have been relatively complicated in design and problem prone in operation. They also often are mechanically inefficient and do not permit precision control of valve pin movement.
Since the plastic injection mold apparatus typically is operated at temperatures in the range of 500-700.degree. F., the valve pin actuator cannot contain lubricant, which may leak and contaminate the flow stream. As a result, relative movement of the actuator parts causes wear and erosion over time, which can effect the shut-off position of the valve pin. Periodically it is necessary to recalibrate the position of the valve pin and/or replace the valve pin and actuator, which may require substantial disassembly of the mold apparatus.
Existing valve gate nozzles, furthermore, channel the flow of the melt stream along the valve pin, which can create a build up about the valve pin and impede reliable operating movement. Because of the high operating temperatures, the nozzles and the mold plates incur temperature expansion and contraction, which also can result in undesirable leakage and contamination about the nozzle. In the event of malfunction or leakage, the manifold must be, disassembled, which can cause costly interruptions in mold operation. Repairs to the valve gate nozzles and their actuators also can be time consuming and expensive.